Photographic process and product



Feb. 2, 1960 E. H. LAND 2,923,623

PHOTOGRAPHIC PROCESS AND PRODUCT Filed March 14, 1955 I Film Supporl S+m+um of Cellulose Acetate Hydrogen Phthulote Phol'osensii'ive Elemen'l Phoi'osensi-l'ive Silver Halide Sl'ra'l'um Alkaline Processing Liquid Shipping Layer |5 YA{ Silver Precipil'a'l'ing Layer Wal'erproof Subcoai' Base Receiving INVENTOR ATTORNEYS United States Patent 6 PHOTOGRAPHIC PROCESS'ALND PRODUCT v Edwin H. Land, Cambridge, Mass.', assignor to Polaroid Corporation, Cambridge, .Mass., ;acorporation of Delaware This invention relates to photographic processes and products and; more p articularl'y,.has.- reference to, improvements in silver halide transfer-reversalsprocesses-and tilrn units useful in carrying out the'sam'e.

This application is a continuation-impart of'my copending application Serial No. 448,441, filed August '9, 1954, which, inturn, is a continuation-in-part of my application Serial No. 176,961, filed'August 1,' 1950, and now abandoned.

In one type. of. silver halide transfer process, athin layer of an alkaline processing solution comprising a silver halide developer, asilver halidet'ransfer agent and an organic film-forming material is provided between the superposed surfaces of a photoexposed gelatin silver halide stratum of a photosensitive element and a stratum of image-receptive material provided onpa print-receiving element. Developer and transfer agent" are" permeated into the silver. halide stratum by the'ahs'orption of'liquid from said layer of solution into the' photosensitive element'where the developer reduces latent image silver halide to silver and the transfer agent reacts with unreduced silver halide to form soluble silver complexes which are difiusibl'e from the photosensitivestratum, and through the layer ofsaid alkaline solution to be'deposited on the image-receiving stratum. These: complexes deposited'on the print-receiving element are there reduced to silver toprovidea reverse image of th'elatent image formed in the photosensitive stratum followingwhicli the photosensitive and print receiving elements are separated withthe layer of processing solution, now in the form of a-film, adhered'tooneor the'other of'said' elements;

In transfer processes as usually carried out, theabsorption into the photosensitive element of liquid from the layerof processing solution is continuous throughout the period needed to provide the transfer imageand results in amore or less gradual reduction in thethickness-ofthe layer of processingsolution. Li'quidabsorption in 'silver halide transfer" processes occurs for the most part in the silver halide stratum. Finally,;the-absorptionof liquid from-thel'ayer of processing solution during the processing period facilitates the formation-of the solid content of the processing-solution intoa film which can be stripped as a unitwith either the photosensitive element or the print-receiving-elementupon" the separation of 'said'elements:

Certain benefits are derivedina transfer processwhen the rate or volume of the liquid absorption is increased. For example, a high order ofabsorption leads to the attainment of a substantially dry transferprint. Also, the reduction in the thickness of the layer'o f processing solution which results from absorption reduces the distance through whichsilvercomplexesmusttravel to reach the print-receiving element with consequent minimization of the lateral diffusion-of said complexes whereby to obtain a transfer print of highresolution.v

The present invention is directedttot achieving these beneficial advantages by theutilizationi of practices which make it possible to absorb avolume fnligl1ld int0lh ice 2. photosensitive element as a. wholev that is.v greater than: the volume of,1iquid absorbable. into/the. silver halide stratum by itself, and which tend to. accelerate the; ab sorption and consequent reduction in the thickness of the layer ofprocessing solutionrs Inrthis regard, it-,should bel noted thatthis invention deals withmasses, of liquid and" solids of small; volume and thicknesses, in. thatthe silver halide stratum may have a thickness of only a fraction of a micron and the layer- 114? of procfissingsolu: tion is limited to a liquidvolumesuch astosallowittq be, formed' into a layer having an initial thickness of from .002 to .003 inch only. Under these circumstances, it Will'be realized that liquidfabsorbedinto the'photor sensitivevstratum to replace any volume of; liquid'with1 drawn from the photosensitive stratum and into'an en: vironment' onv the side thereof *remote from tl fielayer 14 of processing solution will effect a high order ofi'reduction in the thicknessof said layer 14'. f

To this end, the invention emplo s an, absorption mechanism for removing liquid absorbed into the silver halide stratum through that; face thereof which is fillthest from the layer of processingsolution, whereby more liquid from said layer of processing solution becomes available for absorption andis absorbed'into the silver halide stratum; Advantageously, this absorption mechanisrnis'gcarried outwith'a' medium capable of providing; on a photographic film support,v a subcoat adaptedlfor carryinga gelatin" silver halide emulsion stratum of substantiallyi uniform thickness andofprotecting the" silver halide stratum from penetration thereof by impurities which arecontained inwthephotographic support and which tend to desensitize or, otherwise contaminate the photosensitive silver halide.

Accordingly, one'object ofthe present invention is to 7 provide a photographic silver halide transfer-processemploying thesteps of'forrning a liquid layer of an alkaline processing solution comprisinga silver halide developer and a silver halide-transfer 'agent' between the superposed faces of a print-receiving elemeritand aphotoexposed silver halide stratum; absorbing liquid from said layer into and through said silver halide stratum andinto a stratum of a material which is substantially water impermeable or at least diflicultly'permeablev to water but which is swellable by'and permeable to, alkalinepsolutions whereby; as-a result of said absorption; a reduction of a high order in the thickness'ofthe layer of processingsolution is eltected, during saidliquid absorption, developing latent image-silver halide to silver and forming silver complexesin the silver halide stratum with liquid present therein, and transferringat least a part of said silver complexes toward saidprint-receiving element; by diffusion from the photosensitive element, and reducing:said silver complexesto silver adjacent said print-receiving elementz'to provide areverse image of the latent: image; in the photoexposedi silver halide stratum.-

Other objects of the; invention are to: provide silver halidetransfer processes of, the character setforth wherein said processing liquid. absorbed into: said; stratum; of material which; is. resistant topenetration by. water but which. is. penetrable. by alkaline solutions; is penetrated therethrough and into contact with a photographic film support, and" especially to processes which utilize a film support of a porous material capable of absorbing alkaline processing solution in contact therewith wherebyto enhance the ability of the photosensitive elementto absorb the processing" liquid; to'providethe previously de'scribed absorption mechanism in processes-which utilize aprintreceiving element having an image-receptive stratum supportedupon astratum of amaterial which issubstantially impervious tothe alkaline processing solution; as well as iniproicesses whereinthe transfer images is formed in. the layer; ct processing solution; betwcenthe photosensitive and print-receiving elements or partially in said layer and in the print-receiving element.

Another object of the invention is to provide a method of forming and using a photosensitive element having a built-in absorption mechanism of the character described to the end of providing a transfer image in 'a print-receiving element employed in conjunction with the photo sensitive element.

Further objects of the invention are to provide a photographic. product for carrying out a silver halide transfer process which comprises a photosensitive element having a photographic film support, a stratum of a material which is substantially impermeable or at least difiicultly permeable to water but is permeable to alkaline liquids and which is carried on one side of the photographic film support with a photosensitive silver halide stratum carried on the first-mentioned stratum on the side thereof furthest from the photographic film support and providing an outer face of the photosensitive element for use withja print-receiving element and especially a print-receiving element having an image-receptive stratum providing an outer face thereof and which is so associated with the'photosensitive element as to permit the outer faces of the two elements to be positioned in superposed relation for confinement therebetween of a thickened alkaline liquid processing solution comprising a silver halide developer and a silver halide transfer agent spreadable between the faces to carry out the processing of the product; and to provide photographic products of the character set forth wherein said photographic film support is porous and capable of absorbing liquid permeated through the water-resistant but alkali-permeable stratum, and wherein the image-receptive stratum of the printreceiving element is supported upon a stratum or subcoat of a material which is substantially impervious to the alkaline processing solution.

Otherobjects of the invention will in part be obvious and will in part appear hereinafter.

The invention accordingly comprises the several steps and the relation and order of one or more of such steps with respect to each of the others, and the product possessing the features, properties and the relation of elements which are exemplified in the following detailed disclosure, and the scope of the application of which will be indicated in the claims.

For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description taken in connection with the accompanying drawing wherein a preferred'embodiment of a photographic product useful in carrying out the invention isdisclosed, in exaggerated cross section, in a condition undergoing processing in accordance with the nventlon.

In the drawing, a layer 14 of an alkaline processing liquid comprising a solution of a silver halide developer and a silver halide transfer agent, to which there has been added a viscosity-imparting agent, is shown as formed and confined between the superposed faces of a photosensitive element and a print-receiving element 12 which are shown as arranged in a sandwich type of structure and which together provide a preferred embodiment of a film unit employable for carrying out a silver halide transfer-reversal process. Examples of suitable agents for thickening the processing solution include a water-soluble polymer such as a plastic, starch or gum or a material such as an insoluble emulsifiable oil;

Photosensitive element 10 comprises a photographic film support 1012, one side of which is subcoated with a material which is substantially water impermeable or at least diflicultly permeable to water but which is swellable by and permeable to alkaline liquids to provide a stratum 10b. A suitable gelatin silver halide emulsion is supported on the face of the stratum 10b furthest from the 4 photographic film support to provide a photosensitive stratum 10c.

A print-receiving element 12 of a preferred construction is illustrated as comprising a base 13 which as shown is of a liquid-permeable material and carries on one face thereof a subcoat or stratum 16 of a material which is substantially impervious to water and to the processing solution. Print-receiving stratum 15 is supported on the impervious subcoat 16. The stratum 15 of image-receptive material is shown as comprising a stripping layer 15a, constituting the outer surface portion of stratum 15 and a silver precipitating layer 15b. Both the stratum 15a and the stratum 15b are permeable to the processing solution. However, it should be observed that only a surface portion of element 12, namely, the stratum 15, is capable of being permeated to any appreciable extent by the ionic reagents contained in the processing solution. It will be appreciated that the base 13 may comprise a liquid-impervious material such as a conventional plastic photographic film base material. If base 13 is substantially liquid impermeable, stratum 16 may be just an integral extension of the base, in which case no line of demarcation, as shown in the drawing, will actually exist between the layer 16 and the base 13.

The film unit provided by photosensitive element 10 and the print-receiving element 12 is constructed and arranged, as will be well understood to the art, so that the elements 10 and 12 may be brought into superposed relation with the outer surface of the photosensitive stratum 10c and the outer surface of the stratum 15 of image-receptive material in facing relation to each other following the exposure of the photosensitive element 10 in suitable camera apparatus.

By one practice, processing of the exposed film unit proceeds by drawing photosensitive element 10 and the print-receiving element 12 between a pair of pressureapplying rolls so as to superpose the elements 10 and 12 in desired relation to each other and to effect the spreading of a processing solution, introduced between the elements as they are drawn through the pressureapplying rolls, whereby to form a layer 14 of processing solution of a thickness of approximately .002 to .003 inch. Alternativelyjthe processing solution is coated on the outer face of the photosensitive stratum or onto the outer face of the print-receiving stratum 15 or onto both of these just-mentioned strata, following which the photosensitive element 10 and the print-receiving element 12 are brought into superposed relation and are pressed together. Processing of the film unit after its exposure is in all instances carried out in the absence of light or radiation actinic to the photosensitive stratum.

More specifically, a typical processing liquid of suitable alkalinity, i.e., a pH of at least 8 or 9, comprises a solution of a silver halide developer such as hydroquinone and a silver halide transfer agent such as sodium thiosulfate which is thickened to a viscosity ranging from 100 to 200,000 centipoises at 20 C. by the addition of an agent such as a water-soluble polymer, e.g., a plastic material such as sodium carboxymethyl cellulose, starch or gum or which is thickened by an agent such as a water-insoluble emulsifiable oil present in the liquid as the internal phase of a water-oil emulsion. A typical formulation of the processing solution comprises:

G. Water 1860 Sodium carboxymethyl cellulose 93.0

Sodium sulfite 78.0

Sodium hydroxide 54.6 Sodium thiosulfate 14.5 Hydroquinone 52.0 Sodium sulfate 52.0

Developer and transfer agent from the layer of alkaline processing solution 14 are permeated into the silver halide stratum by the absorption of liquid from said layer of solution. Additionally, liquid thus absorbed into I fele neiit.

ass-3,622;

eeessieg solution it, came imejeenta'a jwith'the stratum o-t lmaterial b and because of the nature o'f the stratum 10!; are absorbedtherein.

As liquidis withdrawn from the photosensitive stratum 10c, moreliquid from the layer of processing solution is absorbed into the photosensitive "stratum. The absorption mechanism provided by the stratum 10b is enhanced by an auxiliary absorptioh inechanis'm pfroyided by the photographic filrn support 10a in instances where the film support 'is of a porous hera'tee capable of absorbing liquid from the a processing solution. With the photographic filni support me is of a porou's' inaterial, it will absorb liquid which has penetrated through the stratum 19b. wane liquid absorbed by this mechanism into the support (ia may cause the support to be'e 'me damp to the touch, it should be observed that the quantity 'ofliq'uid thus absorbed is relatively small and furthermore that .in most instances theyphotosensitive element 10, following processing of the film unit, will usually be destroyed or thrown away. V n

i In all instances, the removal of liquid from the photosensitive stratum 10c by any absorption mechanism of the character described places the photosensitive stratum a condition to absorb more liquid from the layer 14 of preee sin'gselutieaq It will thus be appreciated that by the use of a built in absorption mechanism, the photosensitive element is able to absorb tnoreliquid from the layer 14 than it would if lit consisted solely of a support having anemnlsion stratum thereon. The ability of the photosensitive eleinenttoabsorb a "greater volume of viquid than we'umnemany be 'absorbable into the photosensitive stratum not only carries out an efii'cient and high order of reduction in the thickness of the layer 14 of processing solution but tends to do so at 'an accelerated rate. While the thickness of the layer 14 of processing solu' tion, is undergoing reduction by reason of ab'so'rp'tionof liquid therefrom into the photosensitive element 10, developer present in liquid in the silver halide "stratum 're ,dee's latent imagesnv 'r halide to silver, While transfer agent present in"th e photosensitive stratum reacts with iinredueed s'ilver halide to form soluble silver complexes. In the preferred embodiment of the film unit, these complexesdiffuse from the. photosensitive stratum'10'c and throughfthe layer of alkaline processing solution 14 and aiede'pe'sif a en the image-receiving stratum where they fare i'e'duced "to silver to provide the transfer iin'age. following this, the phfo'tosens'i'tive and print-receiving eleji'ents are se ara ed withth'elay'er '14 of processing spintion, which this "time has become formed into a film,

"to the photosensitive sfiatum dr w the image- 'Jr'e p e. 's't'ratnfijn. n e e seatmem o the invention illustrated, the layer 1'4 o f processing solution will be adhered to the photosensitive element "as will more present ly be pointed out in detail. I I s will er inafter be pointed buy, by suitable modificapractices irniay ne carried outfso that the transl l V 15%! d i i 2 S l Patt ,ly i hat er arid n the print receiving e ent. Under thesfe'fcircums'tanees, the layer of processing solution 'ma'ybe stripped "away from the photosensitive element as an integral part of the print 'receiving The preseiitjinvention' is s'pecially suited for carrying out "a silver halide transfer-reversal "p'r'ocesswith a phog5 "'aphif in unit wherein th'e photosensitive "element l visam n si j a' ie an qe b or s 1 teg'raphichImisupporQLfri fe'xarnpleypape'r, which carries an extremely thin gelatin silver halide emulsion stratum having a thickness of the order of from a fraction bfj a '6 mieron r temmicrpn for sligntly'more and whereinthe print-receiving element thereof comprises a stratum of an image receptive material which is extremely thin and of the order'of from less than 1 micron to 3 microns or more and which is supported upon a subcoat or base that is substantially impervious to the liquid, processing solution. However, it will be understood that the enhanced abso'r'ption obtained by the utilization of a special absorption mechanism comprising the stratum 10b may be uti lized in conjunction with a photographic filmsuppo'rt'lfla which is substantially impervious "tothe processing solution as well as in conjunction with thicker emulsion strata than those previously indicated. and that such combinations are employable with a print-receiving element such as the element 12"or witha prin't receiving element com prising a silver precipitating la'yer carried on a paper support and without the use of'the liquid-impervious sub"- coat 16. I e I I From the standpoint o'flo'wer material costs and expense, it is highly desirable to employ a paper support for a photosensitive emulsion. However, a paper support presents certain well recognized disadvantages. For example, it is difii'cult to 'provide'a photosensitive stratum of a substantially uniform thickness on unsi'red paper because of the penetration of the gelatin emulsion into the pores of the paper. Additionally, the paper is absorbent to water and moisture contained in the emulsion when it is coated. Water thus absorbed into the paper support is likely to dissolve impurities therein and carry them in solution into the emulsion layer. This condition is undesirable because these impurities tend to and frequently do effect the desensitization of the emulsion or otherwise contaminate it. v I

As heretofore pointed out, the medium employed in providing the absorption mechanism of this invention is useful in conjunction with a porous film support such as unsized paper which makes it possible to provide a photosensitive silver halide stratum thereon of uniform thickness and which further makes it possible to preventor avoid desensitization of thephotosensitive material.

By reason of the nature of the material which provides the stratum or subcoat 10b, namely, that this material is substantially water impermeable or at least difiicultly permeable to water, it will be appreciated-that this stratum provides an eifective means for preventing impurities in the support from being introduced into a silver halide emulsion stratum coated on stratum 10b. Furthermore, the material of stratum 10b provides a structure on the porous and absorbent support in the nature of a solid film which is substantially impenetrable by the gelatin emulsion and which consequently makes it possible to coat on stratum 10b an emulsion stratum of substantially uniform thickness. v

A further understanding and appreciation of the concepts hereof may be gained from a consideration of the materials and constructional details employed in connection with the film units of this invention.

In a preferred embodiment-and 'as heretofore indicated, the film support 10a is a porous and absorbent paper in an untreated and unsized condition of which unsized and untreated Alpha paper is an example. Other vpapers of suitable absorbing qualities may, however, be employed. Alternatively, although not as preferred, the support 10a may comprise any conventional photographic film support of an. organic plastic which is substantially impervious to the alkaline processing solutions and to water. i 1

In more detail, properties of the material satisfactory for providing the stratum 1% on the film support 1011 or at least difiicultly permeable to water while being swellable and permeable to alkaline liquids of the nature of the processing solut'ion employed hereim Also,

the material ot str'aturn 10b should be of a'naturesolubl'e '7 in conventional organic solvents so that it is coatable in a solution thereof onto a supporting surface to provide a stratum or subcoat thereonwhic h, upon evaporation of the solvent liquid therefrom, forms a solid film adhered to said surface. I

A preferred example of a suitable material for stratum b is a commercially available cellulose acetate hydrogen phthalate which has a combined degree of substitution by acetate and acid phthalate substituents of a nature to cause this compound to possess the desired properties just detailed. The term cellulose acetate phthalate is commonly applied to cellulose esters of this nature which may have one carboxyl of phthalic acid combined with the cellulose as well as to esters of this nature which may have both carboxyl groups of the phthalic acid combined with the cellulose. The preferred material for carrying out this inventionis the acid form of cellulose acetate phthalate, namely, the form thereof where only one carboxyl of the phthalic acid is combined with cellulose while the other carboxyl has a free hydroxyl group and for more precise identification, this ester of cellulose isreferredto in the specification and claims as cellulose acetate hydrogen phthalate. Suitable cellulose acetate hydrogen phthalates possessing the foregoing characteristics are found among those described in an article entitled Cellulose Esters of Dibasic Organic Acids by Carl J. Malm'and Charles R. Fordyce appearing in Industrial and Engineering Chemistry, volume 32, page 405, 1940, and also in US. Patent No. 1,954,337, issued to Cyril I. Stand, April 10, 1934.

Other examples of suitable materials for stratum 10b include polyvinyl hydrogen phthalate and easily saponified organic film-forming materials such as shellac and Japan wax.

Malm and Fordyce point out in the just-mentioned article that most cellulose acetate hydrogen phthalates are soluble in dilute sodium hydroxide. On the other hand, the previously mentioned Patent No. 1,954,337 suggests that sodium sulfite present in a conventional silver halide developing solution permeated into a stratum of cellulose acetate hydrogen phthalate will inhibit solution of the cellulose acetate hydrogen phthalate in the permeated liquid. However, such dissolution as may occur of the cellulose acetate hydrogen phthalate employed by this invention may be treated as unobjectionable due to the type of the photographic processing carried out.

In this regard, it should be noted that the stratum 10b of material is never immersed in an alkaline solution and that the layer 14 of the alkaline processing solution is only a few thousandths of an inch thick at the time of its formation. From this, it follows that the maximum volume of liquid permeable through eachunit area of the face of the photosensitive element in contact withthe layer 14 of processing solution is at best minute and that the volume of liquid absorbable from the photosensitive stratum 10c into stratum 10b will be even smaller and of an order unfavorable to the com plete dissolution of the material of stratum 10b.

Furthermore, such dissolution of the material of stratum 10b as may occur will advantageously accelerate the removal rate of liquid from the photosensitive stratum 10c as well as the thinning out of the layer 14 of processing solution and in instances Where the film support 10a is of an absorbent character, will facilitate. the removal of liquid from the stratum 10b into an environment where this liquid will tend, toremain until dissipated by evaporation.

In addition, it should be kept in mind that the type of processing employed maintains a sandwich type of structure until the completion of image formation. For all practical purposes, the sandwich structure may be considered as a closed system which is capable of confining the processing liquid during the processing period. By the time that image formation in the sandwich has become complete, substantially allot the liquid inthe sandwichhas become evaporated or it has become absorbed in one 'or more outer layers thereof and thelayer 14 of processing solution has become 'solidified. "The withdrawal of liquidfrom the stratum 10b resulting from either or both of these removal mechanisms is effective to return the stratum to a firm or solidified condition.

A suitable composition for providing stratum 10b comprises 4 grams of cellulose acetate hydrogen phth alate in solution in a mixture of 20 cc.'of methanol and cc. of actone. If a stratum of greater thickness is desired, the concentration of the cellulose acetate hydrogen phthalate in the foregoing solution may 'be increased, or a second application of the. coatingsolution of the previously detailed composition is applied after the first-coated material has-thoroughly 'dried. While organic solvents from the mixture may penetrate into the photographic film support, any impurities transported in solution from the support will be. retained in stratum 10b which is, allowed to thoroughly dry before the gelatin silver halide photosensitive stratum-10c is coated thereon. I Photosensitive element 10, illustrated in the drawing, is especially adapted for employment with extra fast gelatin silver halide emulsions. High-speed emulsions are coated in extremely. thin layers of the order of a fraction of a micron to 4 microns or slightly more as heretofore indicated. The products of' the present invention are particularly useful in improving the results obtained when the transfer process is carried out with one of the high-speed photosensitive silver halide emulsions such as the emulsion of the relatively high-speed orthochromatic films, e.g.', Eastman Kodak v\lerichrome film, having an ASA speed ratingxof 0200 and an ASA exposure index rating in the daylight' of 50, and the extremely high-speed panchromatic emulsions, e.g., Eastman Kodak Super XX'Pan having an ASA speed rating of 0400 and an ASA exposure index'ratingin the daylight of 100, and. Ansco Triple S Pan. Also satisfactory are the emulsions of Kodak Photofiure Safety films'and Du Pont High Speed Pan film. It is also to be kept in mind that the productsand processes of the present inventionare also useful with slower emulsions and when so used give. excellent results. Such emulsions, for example, comprise.Contrast Process Ortho film or the emulsions of chloride and chlorobromide type printing and'enlarging papers. The slower emulsions will, of course, be provided by relatively thick strata of the nature, for example, of from 30 to 40 microns. I v

In a preferred embodiment, the print-receiving element 12 employs a base 13 comprising a water-permeable material such as unco'ated or gelatin coated paper,-for example baryta coated paper, or the base may comprise a substantially water-impermeable material such, for example, asunplasticized polymethacrylic'acid or onejof the cellulo'sic esters, such as cellulose nitrate, cellulose acetate, cellulose butyrate, cellulose propionate, cellulose acetate butyrate or cellulose acetate'propionate. Preferred, however, are the rubbery typesfof plastics 'such as polyvinyl butyral. i j v f As heretofore mentioned, if ba'se 13 is liquid permeable, stratum 16 constitutes a separate liquid-impermeable film comprising one of the just-named water-impermeable materials and is coated on the support. Also, as previously mentio'ned, if the base 13 is substantially water impermeable, the stratum 16'may' be justan integral extension of the base. I i v The stratum 15 of image-receptive material, as previously indicated, comprises a layer 15b coated on' base 13 and a stripping layer 15a coated on layer 15b. Layer 15b comprises a matrix of a water-insoluble inorganic adsorbent substance such as silica in which there is incorporated suitable, silver precipitating agents, such, fofexample, as the metallic, sulfides and selenides and heavy meal a v a The layer 15a provides a stripping layer of a nature such that the layer 14 of processing solution will, upon solidification, become adhered thereto by a weaker bond than the bond between said layer 14 and the silver halide stratum 100. Thus, the layer 14 of processing liquid will remain adhered to the photosensitive element in the illustrated embodiment of film unit when the photosensitive element and the print-receiving element are separated. Suitable materials for providing stripping layer a comprise gum arabic, sodium alginate, pectin, cellulose acetate hydrogen phthalate, polyvinyl alcohol, hydroxyethyl cellulose or polymethacrylic acid and, when kept very thin, may be of plasticized methyl cellulose, ethyl cellulose, methyl methacrylate or butyl methacrylate.

Print-receiving elements embodying the preferred construction illustrated in the drawing are detailed in connection with my copending application Serial No. 234,622, now Patent No. 2,823,122, filed June 30, 1951.

As an alternative construction, the film unit may be so designed that the layer 14 of processing solution when solidified will remain adhered to the print-receiving element upon separation of the film unit. For example, the stripping layer 15a disclosed in the drawing may be omitted. This alternative construction is useful in instances where the silver complex is transferred by diffusion from the photosensitive element toward the printreceiving element and the complex is at least in part reduced to silver in the layer of processing solution. United States Patent No. 2,662,822, issued to Edwin H. Land on December 15, 1953, discloses a suitable print-receiving element and practices for carrying out this concept of the invention.

Additionally, the concepts of this invention may be practiced with modified embodiments of print-receiving elements. Thus, the liquid-impermeable subcoat 16 may be omitted and the print-receiving stratum 15 comprising the layers 15a and 15b, or merely the layer 15b of imagereceptive material containing the silver precipitating agents may be applied directly to a liquid-permeable film base such as one of the papers heretofore mentioned.

Throughout the specification and the claims where the terms alkali-permeable material, alkali-permeable stratum" and similar expressions are employed, there is meant a stratum or a material which is permeable to aqueous alkaline liquids or solutions. In distinction to the terms alkali-permeable material, alkali-permeable stratum and similar expressions, the term water-impermeable where used in the specification and the claims is intended to refer to a material or a stratum which is substantially impermeable to aqueous liquids or solutions which are neutral or acid.

Since certain changes may be made in the above product and process without departing from the scope of the invention herein involved, it is intended that all matter contained in the above description or shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. In a photographic product for carrying out a silver halide transfer process, in combination, a photosensitive element comprising a photographic film support, a stratum of a material which is substantially impermeable to water but permeable to alkaline liquids carried on one side of said photographic film support and a photosensitive silver halide stratum carried on the first-mentioned stratum on the side thereof furthest from said photographic support and providing an outer face of said photosensitive element; and a print-receiving element having an outer face andbeing so associated with said photosensitive element as to permit said outer faces of said elements to be positioned in superposed relation for the confinement therebetween of an alkaline liquid solution of a silver halide developer and a silver halide transfer agent spreadable between said faces to carry outthe processing of said photographic product, said material which is impermeable to Water but permeable to alkaline liquids being cellulose acetate hydrogen phthalate.

2. A photographic product as defined in claim 1 wherein said photographic film support is porous and capable of absorbing liquid permeated through said stratum of material which is substantially impermeable to water but ermeable to alkaline liquid.

3. A photographic product as defined in claim 2 where in said photographic film support is paper.

4. A photographic product as defined in claim 1 wherein said print-receiving element is provided with an imagereceptive stratum adjacent that face thereof which is positionable in superposed relation to said photosensitive element, and wherein said image-receptive stratum is carried upon a stratum of material which is substantially impervious to water and alkaline liquids.

5. A photographic product as defined in claim 4 wherein said photographic film support is paper capable of abso'rbing alkaline liquids.

6. In a photographic silver halide transfer process, the steps which comprise forming a layer of an alkaline solution of a silver halide developer and a silver halide transfer agent between one face of a print-receiving element and one face of a photosensitive element located in superposed relation to the print-receiving element, said pho'tosensitive element being photoexposed to provide a latent image, said photosensitive element comprising a photographic film support composed of a paper material, a stratum of material containing a film-forming polymeric acid, the last-mentioned material being substantially water impermeable but permeable to alkaline liquids and being carried by one side of said support and a photoexposed silver halide stratum carried by the surface of the waterimpermeable but alkali-permeable stratum furthest from said support; absorbing said solution into said silver halide stratum and through said silver halide stratum and into the stratum of said water-impermeable and alkalipermeable material, and, as a result of said absorption, increasing the rate and the amount of the reduction of the thickness of said layer of solution; by means of said solution present in said silver halide stratum, developing latent image silver halide to silver and forming silver complexes soluble and transferable in said solution from said photosensitive element toward said print-receiving element; transferring said silver complexes toward said print-receiving element by diffusion from said photosensitive element; and reducing said silver complexes to silver adjacent the said face of said print-receiving element to provide a reverse image of the latent image formed in said photosensitive element, said stratum of material which is water-impermeable but permeable to alkaline liquids comprising cellulose acetate hydrogen phthalate.

References Cited in the file of this patent UNITED STATES PATENTS 1,954,337 Stand Apr. 10, 1934 2,543,181 Land Feb. 27, 1951 2,559,643 Land July 10, 1951 2,565,377 Land Aug. 21, 1951 2,698,798 Land Ian. 4, 1955 2,774,668 Rogers Dec. 18, 1956 

6. IN A PHOTOGRAPHIC SILVER HALIDE TRANSFER PROCESS, THE STEPS WHICH COMPRISE FORMING A LAYER OF AN ALKALINE SOLUTION OF A SILVER HALIDE DEVELOPER AND A SILVER HALIDE TRANSFER AGENT BETWEEN ONE FACE OF A PRINT-RECEIVING ELEMENT AND ONE FACE OF A PHOTOSENSITIVE ELEMENT LOCATED IN SUPERPOSED RELATION TO THE PRINT-RECEIVING ELEMENT, SAID PHOTOSENSITIVE ELEMENT BEING PHOTOEXPOSED TO PROVIDE A LATENT IMAGE, SAID PHOTOSENSITIVE ELEMENT COMPRISING A PHOTOGRAPHIC FILM SUPPORT COMPOSED OF A PAPER MATERIAL, A STRATUM OF MATERIAL CONTAINING A FILM-FORMING POLYMERIC ACID, THE LAST-MENTIONED MATERIAL BEING SUBSTANTIALLY WATER IMPERMEABLE BUT PERMEABLE TO ALKALINE LIQUIDS AND BEING CARRIED BY ONE SIDE OF SAID SUPPORT AND A PHOTOEXPOSED SILVER HALIDE STRATUM CARRIED BY THE SURFACE OF THE WATERIMPERMEABLE BUT ALKALI-PERMEABLE STRATUM FURTHEST FROM SAID SUPPORT, ABSORBING SAID SOLUTION INTO SAID SILVER HALIDE STRATUM AND THROUGH SAID SILVER HALIDE STRATUM AND INTO THE STRATUM OF SAID WATER-IMPERMEABLE AND ALKALIPERMEABLE MATERIAL, AND, AS A RESULT OF SAID ABSORPTION, INCREASING THE RATE SAND THE AMOUNT OF THE REDUCTION OF THE THICKNESS OF SAID LAYER OF SOLUTION, BY MEANS OF SAID SOLUTION PRESENT IN SAID SILVER HALIDE STRATUM, DEVELOPING LATENT IMAGE SILVER HALIDE TO SILVER AND FORMING SILVER COMPLEXES SOLUBLE AND TRANSFERABLE IN SAID SOLUTION FROM SAID PHOTOSENSITIVE ELEMENT BY DIFFUSION FROM SAID PHOTOSENSIELEMENT, TRANSFERRING SAID SILVER COMPLEXES TOWARD SAID PRINT-RECEIVING ELEMENT BY DIFFUSION FROM SAID PHOTOSENSITIVE ELEMENT, AND REDUCING SAID SILVER COMPLEXES TO SILVER ADJACENT THE SAID FACE OF SAID PRINT-RECEIVING ELEMENT TO PROVIDE A REVERSE IMAGE OF THE LATENT IMAGE FORMED IN SAID PHOTOSENSITIVE ELEMENT, SAID STRATUM OF MATERIAL WHICH IS WATER-IMPERMEABLE BUT PERMEABLE TO ALKALINE LIQUIDS COMPRISING CELLULOSE ACETATE HYDROGEN PHTHALATE. 